The present invention relates to a shadow mask type color cathode ray tube, and in particular to a color cathode ray tube of the type having its shadow mask supported at its corners.
As image or video display devices, shadow mask type color cathode ray tubes are widely used which employ a shadow mask which is formed with a large number of electron-transmissive apertures and serves as a color selection electrode.
A color cathode ray tube of this kind has an approximately rectangular panel portion having a spherical, flat or approximately flat outer surface and an inner surface which is convex toward the outer surface. Formed on the inner surface of the panel portion is a phosphor screen comprised of phosphor elements of a plurality of colors (usually three colors of red, green and blue) in the form of dots, slots or continuous strips.
An electron gun for projecting a plurality (usually three) of electron beams onto the phosphor screen is housed within a neck portion of the color cathode ray tube. A vacuum envelope of the color cathode ray tube is formed by integrally connecting the panel portion and the neck portion with a funnel portion.
Closely spaced from the phosphor screen within the panel portion is a shadow mask structure comprising a support frame (or a mask frame, or referred to merely as a frame) of a generally rectangular shape conforming to that of the panel portion, a generally rectangular shadow mask which is convex toward the phosphor screen and is attached to the support frame at its periphery, and suspension springs to be adapted to engage studs embedded into an inner sidewall of a skirt portion of the panel portion.
In this shadow mask structure, plate-like springs (leaf springs) are attached to the support frame along the sides of the support frame at at least three points of the support frame as by welding. The free ends of the leaf springs are formed with engagement holes which are adapted to engage the studs embedded in the inner sidewall of the skirt portion of the panel portion such that the shadow mask structure is supported and spaced by a specified distance from the phosphor screen.
Usually the leaf springs are attached to the four sides of the generally rectangular support frame, or to three of the four sides, and necessarily studs are embedded at positions of the inner sidewall of the skirt portion corresponding to the engagement holes in the leaf springs.
However, as the size of the viewing screen of color cathode ray tubes has been increasing recently, the weight of the shadow mask structure, and in particular of the support frame has increased and it is difficult for the above-described leaf springs to support the shadow mask structure properly and compensate for its positional deviations caused by thermal expansion of the mask structure sufficiently.
As one of means for reducing the weight of the shadow mask structure, and in particular of its support frame, a method is known to be effective which reduces the thickness and the width of the support frame and attaches suspension springs at the corners of the support frame.
FIG. 9 is a schematic plan view of the shadow mask structure having the suspension springs attached at its corners, as viewed from its electron gun side. A phosphor screen 4 is formed on the inner surface of a panel portion 1. A shadow mask 6 is disposed a specified distance from the phosphor screen 4, and suspension springs 8 attached to the four corners of a support frame 7 engage studs 9 embedded in the inner wall of the skirt portion of the panel portion 1. Lines of action of the suspension springs 8 are arranged approximately in parallel with the tube axis as described subsequently.
FIG. 10 is a perspective view of an exemplary configuration of the suspension springs 8 shown in FIG. 9. In FIG. 10, the suspension spring is generally designated as 8. Zxe2x80x2xe2x80x94Zxe2x80x2 denotes its line of action which is approximately parallel with the longitudinal axis of the color cathode ray tube. The suspension spring 8 is formed by fixing an end of a spring member 82 to an end of a base member 81 as by welding. The fixed portion is indicated as a joint portion (a laminated portion) 83.
The base member 81 has a sloped portion 812 formed to make a small angle with respect to a flat portion 811 to project upwardly. The flat portion 811 is fixed to the support frame of the shadow mask structure. In this example, the flat portion 811 is formed with stepped portions 813. The stepped portions 813 are adapted to be inserted into slits (not shown) formed in the support frame such that locations of the suspension springs are determined and thereby the operation of attaching the suspension springs 8 is facilitated.
However, provision of the stepped portions 813 is not essential, or other means such as protrusions can be used for locating the suspension springs 8. The base member 81 can be made in the form of a flat plate, and can be welded directly to the sidewall of the support frame.
The spring member 82 has a flat portion 821 and a sloped portion (an operating portion) 822 extending from the flat portion 821 to the joint portion 83. The flat portion 821 is formed with an engagement hole 825 to be adapted to engage a stud (not shown). A washer is sometimes disposed between the stud 9 (see FIG. 9) and the engagement hole 825, but the washer is omitted in this specification.
Incidentally, a tab 823 is provided at an end of the flat portion 821 mainly for the purpose of rotating the spring member 82 in a direction indicated by an arrow xe2x80x9cAxe2x80x9d against resiliency of the sloped portion 822 in removing and remounting of the shadow mask structure by using a robot or manually. The tab 823 is not always necessary if the shadow mask structure can be removed and remounted by using the flat portion 821.
A conventional color cathode ray tube employing suspension springs of this type for supporting its shadow mask at its corners is disclosed in Japanese Patent Application Laid-open Hei 5-89793, for example.
It is a representative one of the objects of the present invention to provide a novel color cathode ray tube capable of compensating for a doming phenomenon occurring in a shadow mask properly and improving efficiency in the operation of removing and remounting the shadow mask structure.
To accomplish the above object of the present invention, in accordance with an embodiment of the present invention, there is provided a color cathode ray tube comprising an evacuated envelope including a generally rectangular shallow dish-like panel portion having a peripheral skirt portion, a tubular neck portion, and a funnel portion for connecting the panel portion and the neck portion, an electron gun housed within the neck portion, a phosphor screen formed on an inner surface of the panel portion, a shadow mask structure closely spaced from the phosphor screen within the panel portion, the shadow mask structure comprising a generally rectangular peripheral support frame, a generally rectangular shadow mask having an apertured portion formed with a multiplicity of electron-transmissive apertures and a peripheral skirt portion, the shadow mask being attached at the peripheral skirt portion thereof to the support frame, and suspension springs attached to corners of the support frame corresponding to the corners of the panel portion, and a plurality of studs embedded in an inner wall of the skirt portion at corners of the panel portion for supporting the shadow mask structure, wherein each of the suspension springs comprises a base member fixed to a corresponding one of the corners of the support frame, and a spring member fixed at a panel-portion side end thereof to the base member; and the spring member includes a resilient sloped portion extending in a direction of a longitudinal axis of the color cathode ray tube from the panel-portion side end of the spring member, and bent toward the skirt portion of the panel portion from the direction of the longitudinal axis of the color cathode ray tube, an engagement portion formed with an engagement hole engaged with a corresponding one of the plurality of studs, and a generally step-like portion provided between the resilient sloped portion and the engagement portion for protruding the engagement portion toward the corresponding one of the plurality of studs such that a center of the engagement hole in a condition thereof engaged with the corresponding one of the plurality of studs is displaced toward the inner wall of the peripheral skirt portion of the panel portion from an intersection of a longitudinal axis of the corresponding one of the plurality of studs with an imaginary plane projected from the resilient sloped portion.
To accomplish the above object of the present invention, in accordance with another embodiment of the present invention, there is provided a color cathode ray tube comprising an evacuated envelope including a generally rectangular shallow dish-like panel portion having a peripheral skirt portion, a tubular neck portion, and a funnel portion for connecting the panel portion and the neck portion, an electron gun housed within the neck portion, a phosphor screen formed on an inner surface of the panel portion, a shadow mask structure closely spaced from the phosphor screen within the panel portion, the shadow mask structure comprising a generally rectangular peripheral support frame, a generally rectangular shadow mask having an apertured portion formed with a multiplicity of electron-transmissive apertures and a peripheral skirt portion, the shadow mask being attached at the peripheral skirt portion thereof to the support frame, and suspension springs attached to corners of the support frame corresponding to the corners of the panel portion, and a plurality of studs embedded in an inner wall of the skirt portion at corners of the panel portion for supporting the shadow mask structure, wherein each of the suspension springs comprises a base member fixed to a corresponding one of the corners of the support frame, and a spring member fixed at a panel-portion side end thereof to the base member; and the spring member includes a resilient sloped portion extending in a direction of a longitudinal axis of the color cathode ray tube from the panel-portion side end of the spring member, and bent toward the skirt portion of the panel portion from the direction of the longitudinal axis of the color cathode ray tube, and an engagement portion continuous with the resilient sloped portion and having an engagement hole engaged with a corresponding one of the plurality of studs, the engagement hole being made in a protuberant central area raised above a surrounding surface of the engagement portion for protruding the engagement hole toward the corresponding one of the plurality of studs such that a center of the engagement hole in a condition thereof engaged with the corresponding one of the plurality of studs is displaced toward the inner wall of the peripheral skirt portion of the panel portion from an intersection of a longitudinal axis of the corresponding one of the plurality of studs with an imaginary plane projected from the resilient sloped portion.
To accomplish the above object of the present invention, in accordance with another embodiment of the present invention, there is provided a color cathode ray tube comprising an evacuated envelope including a generally rectangular shallow dish-like panel portion having a peripheral skirt portion, a tubular neck portion, and a funnel portion for connecting the panel portion and the neck portion, an electron gun housed within the neck portion, a phosphor screen formed on an inner surface of the panel portion, a shadow mask structure closely spaced from the phosphor screen within the panel portion, the shadow mask structure comprising a generally rectangular peripheral support frame, a generally rectangular shadow mask having an apertured portion formed with a multiplicity of electron-transmissive apertures and a peripheral skirt portion, the shadow mask being attached at the peripheral skirt portion thereof to the support frame, and suspension springs attached to corners of the support frame corresponding to the corners of the panel portion, and a plurality of studs embedded in an inner wall of the skirt portion at corners of the panel portion for supporting the shadow mask structure, wherein each of the suspension springs comprises a base member fixed to a corresponding one of the corners of the support frame, and a spring member fixed at a panel-portion side end thereof to the base member; and the spring member includes a resilient sloped portion extending in a direction of a longitudinal axis of the color cathode ray tube from the panel-portion side end of the spring member, and bent toward the skirt portion of the panel portion from the direction of the longitudinal axis of the color cathode ray tube, and an engagement hole engaged with a corresponding one of the plurality of studs is made in a protuberant central area raised above a surrounding surface of the resilient sloped portion for protruding the engagement hole toward the corresponding one of the plurality of studs such that a center of the engagement hole in a condition thereof engaged with the corresponding one of the plurality of studs is displaced toward the inner wall of the peripheral skirt portion of the panel portion from an intersection of a longitudinal axis of the corresponding one of the plurality of studs with an imaginary plane projected from the resilient sloped portion.
The present invention is not limited to the above configurations or the configurations of the embodiments described subsequently, and various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.